Chapter 9: LO
Terms in this set (17)
List various outcomes of muscle actions.
*Provide muscle tone
*Propels body fluids and food
Describe the structure of a skeletal muscle.
- Thick and Thin filaments
- Muscle fiber
- Epimysium around muscle
- Perimysium around fascicle
- Endomysium around muscle fiber
Name the major parts of a skeletal muscle fiber and describe the functions of each.
- I Band: Light band, composed
of thin actin filaments
- A Band: Dark band, composed
of thick myosin filaments overlapping
with thin actin filaments
H Zone: Center of A band;
composed of thick myosin filaments
- Z Line: Anchors filaments in place;
sarcomere boundary; center of I band
- M Line: Anchors thick filaments;
center of A band
- Thick filaments:
Composed of myosin protein; heads form crossbridges
- Thin filaments:
Composed of actin protein; associated with troponin and tropomyosin, which prevent crossbridge formation when muscle is not contracting
Describe the neural control of skeletal muscle contraction.
The cell that releases the acetylcholine is a motor neuron. The acetylcholine binds to chemically gated Na channels. This depolarizes the muscle cell. The SR releases Ca.
Identify the major events of skeletal muscle contraction.
- SR releases Ca
- Ca binds to troponin/tropomyosin
- Troponin/tropomyosin moves to open up the myosin binding site on actin
- myosin head (with ADP and Pi bound) binds to actin
- Myosin head undergoes power stroke which moves the myosin head from an upright position to a low energy state and releases ADP and Pi.
- ATP binds to the myosin head causing it to release the actin
- The myosin head undergoes a recovery stroke - ATP is hydrolysed and the energy released which moves the myosin head to its high energy state with ADP and Pi attached
- The myosin head again binds to the actin filament and the cycle repeats
- Cycle ends when the SR pumps Ca back into its lumen thus decreasing the concentration of Ca in the cytoplasm.
- Ca comes off of troponin/tropomyosin which again covers the myosin binding site on actin.
List the energy sources for skeletal muscle fiber contraction.
- lipids (fatty acids) and carbohydrates (glucose) are the long term energy sources
- short term the energy is stored in creatine phosphate and ATP
Describe oxygen debt.
Oxygen debt is the amount of oxygen needed by liver cells to convert the accumulated lactic acid to glucose and to restore muscle ATP and creatine phosphate concentrations.
Describe how a muscle may become fatigued.
- Inability to contract muscle
Common causes of muscle fatigue:
- Decreased blood flow
- Ion imbalances across the sarcolemma
- Loss of desire to continue exercise
- Accumulation of lactic acid (controversial)
Distinguish between a twitch and a sustained contraction.
A twitch is contractile response of a single muscle fiber to a single impulse and a sustained contractions emits action potentials at a very high rate so it will stay contracted much longer.
Explain how various types of muscular contractions produce body movements and help maintain posture.
- Isotonic muscles contract and change length, contractions stay equal to the force.
- Concentric is muscle shortening
- eccentric is muscle lengthening.
- Isometric reactions contract but do not change length.
Distinguish between fast and slow twitch muscle fibers.
Muscle fibers vary in contraction speed and whether they produce ATP oxidatively or glycolytically. Slow twitch fibers are also called red fibers because they contain red, oxygen-storing pigment myoglobin. An example of red fibers are long muscles of the back. These fibers are well supplied with oxygen-carried blood. Red fibers contain many mitochondria, which is an adaptation for the aerobic reactions of cellular respiration. Red fibers have a high respiratory capacity and can generate ATP fast enough to keep up with the ATP breakdown that occurs during contraction. Since red fibers have high ATP production, they can function for long periods of time without fatiguing.
Fast twitch glycolytic fibers are also called white fibers because they have less myoglobin and have a poorer blood supply than red fibers. An example of white fibers consist of certain hand muscles and muscles that move the eye. These fibers have fewer mitochondria, meaning they have a reduced respiratory capacity. White fibers have a more extensive sarcoplasmic reticulum to store and reabsorb calcium ions. White fiber's ATPase is also faster than red fibers. White muscle fibers can contract rapidly but they are more susceptible to fatigue.
Distinguish between the structures and functions of multiunit smooth muscle and visceral smooth muscle.
Multiunit smooth muscle
•Cells are separate
•Activated by nervous system or hormones
Visceral smooth muscle
•Cells in sheets
•Self activating with waves of contraction in rhythmic pattern.
Compare the contraction of mechanisms of skeletal and smooth muscle fibers.
- skeletal muscles are controlled by Ca being released from the SR. This Ca binds troponin and tropomyosin causing it to move to open up the myosin binding site on actin
- smooth muscles are controlled by Ca being released from either the SR or coming in from outside the cell. Smooth muscle cells do not have troponin/tropomyosin. Instead the use calmodulin and MLCK. Ca binds to calmodulin which binds, in turn, to myosin light chain kinase (MLCK). This kinase phosphorylates myosin light chain which allows the myosin head to bind to actin. The muscle is turn off by the action of a phosphatase which dephosphorylates myosin light chain.
Compare the contraction mechanisms of skeletal and cardiac muscle fibers.
cardiac muscles get calcium from both the SR and from outside the cell while skeletal muscles only use Ca from the SR. This allows calcium channel blockers to effect cardiac muscles.
Explain how the attachments, locations, and interactions of skeletal muscles make possible certain movements.
- Agonist: muscle that causes an action
- Prime mover: agonist primarily responsible for movement
(In some cases, the terms "agonist" and "prime mover" are used interchangeably)
- Synergists: muscles that assist agonist / prime mover
- Antagonist: muscles whose contraction causes movement in the opposite direction of the prime mover
- Fixator: Muscles which holds the bone, which is the point of origin, in place.
Describe aging-related changes in the muscular system.
Myoglobin, ATP, and creatine phosphate decline, starting in the 40s
Connective tissue and adipose cells replace some muscle tissue
By age 80, almost half of muscle mass has atrophied
Muscle strength decreases, and reflexes become slower
Exercise helps to maintain muscle mass and function
New muscle cells can be stimulated to grow from satellite cells in response to IL-6
Discuss how exercise can help maintain a healthy muscular system as the body ages.
Exercise helps maintain muscle mass and function.